Vehicle operators generally prefer to load the maximum amount of freight that their vehicle can carry when undertaking a delivery. Many operators adopt this behavior because they are often paid based on the amount of freight delivered within a certain amount of time. Thus, most operators are motivated to traverse their routes as rapidly as possible with as much freight as they can legally carry.
As vehicles traverse a given route, fuel economy can be significantly influenced by the way an operator selects the vehicle speed. An aggressive operator that creates rapid transitions in speed while maintaining the maximum allowable speed limit through the route (legal, fleet owner imposed, etc.), will likely not achieve maximum fuel economy. Such a driver will prefer to maximize fuel load and freight quantity in order to accommodate their driving pattern.